<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
	<script>
		var bj=10;
		function add(){
		    var bj=20;
		    console.log(this);//window
		    console.log(this.bj);//10
		    console.log(bj);//20
		    console.log(this.bj+bj);//30
		}
		add();
		window.add();
	</script>
</html>
